The most promising approach to the study of the lactose system appeared to lie through genetic analysis. Conjugation had become a useful instrument for the analysis of any bacterial function. Starting from the viewpoint of the phage system, the author wanted Jacques’ opinion about the implications for the lac system of two basic concepts: (1) Repression (or induction) operates not progressively, but like a switch, by a yes-or-no, an on-or-off mechanism that involves only two states; and (2) Genetic units of an order higher than the gene must exist: “units of activity” that contain several genes subject to unitary expression, such expression probably being regulated at the level of DNA. Actually," Jacques concluded, "there is no direct evidence either for or against the idea of repression at the level of DNA, and we should keep this possibility in mind." His objection to the switch, the on-or-off concept of protein synthesis, appeared more serious to the author. During a small meeting in Sydney Brenner's room at King's College, the author described the latest results obtained in Paris and Berkeley on the regulation of protein synthesis and mentioned once again the unstable RNA hypothesis. The whole system could be viewed as an on-or-off switch alternating between two states, just like the switch of the small electric train. In the fall of 1960, Jacques and the author decided to assemble the various pieces of information then available into a story, mainly written by Jacques.